1. Field
The present invention relates to a droplet discharging device of a recording head for use in an atomizer, applicator, and an inkjet recording device, and a particle manufacturing device, such as a powder manufacturing device or a toner manufacturing device, equipped with the droplet discharging device.
2. Background Art
A recording head serving as a droplet discharging device of an inkjet recording device used as an inkjet printer and an inkjet plotter typically discharges ink droplets from multiple nozzle openings by compressing ink in a compression chamber that communicates with the nozzle openings using pressure generating elements such as piezoelectric elements provided for each of the nozzle openings.
For example, a drive signal generator circuit as illustrated in FIG. 5 is known that generates drive signals to drive the recording head of such an inkjet recording device.
The drive signal generator circuit as illustrated in FIG. 5 has a signal generating circuit 81 to output a charge-discharge pulse 80 to regulate the timing of charge and discharge of a pressure generating element 17, a voltage amplifier circuit 82 for the charge-discharge pulse 80, and an electric current amplifier circuit 83 that, based on the charge-discharge pulse 80, outputs to the pressure generating element 17 a common drive signal COM which is amplified by switching operation of an NPN-type bipolar transistor (hereinafter referred to as NPN transistor) Q1 and a PNP-type bipolar transistor (hereinafter referred to as PNP transistor) Q2, which are push-pull connected.
The pressure generating element 17 is a capacitor C1.
When the drive signal COM is applied to the capacitor C1, the pressure generating element 17 repeatedly charges and discharges based on the drive signal COM.
However, in the typical drive signal generator circuit as illustrated in FIG. 5, since a voltage VO corresponding to the voltage difference between a driving voltage Vcc or a ground GND and the drive signal COM is simply applied as is across the collector-emitter of the NPN transistor Q1 or the PNP transistor Q2 when discharging or charging in the electric current amplifier circuit 83, the amount of heat generation of the NPN transistor Q1 and the PNP transistor Q2 is large.
As a result, a large-scale heat discharging device is required to discharge the heat of the NPN transistor Q1 and the PNP transistor Q2, resulting in a larger-than-necessary printer.
JP-2001-063040-A and JP-2011-046028-A disclose an inkjet recording device and a liquid spraying device equipped with a drive signal generator circuit that reduces heat generation by reducing the power consumption of the transistors of the electric current amplifier circuit.
In the inkjet recording device of JP-2001-063040-A mentioned above, as illustrated in FIG. 6, a primary coil L1 of a transformer 90 is electrically connected between the collector of the NPN transistor Q1 of a push-pull circuit 830 and the driving voltage Vcc.
A secondary coil L2 of the transformer 90 is electrically connected between the collector of the PNP transistor Q2 and the ground GND.
This configuration makes it possible to reduce the emitter-collector voltage of the NPN transistor Q1 and the PNP transistor Q2A when charging and discharging.
The liquid spraying device of JP-2011-046028-A mentioned above, as illustrated in FIG. 7, has a (digital) drive signal generating unit 70 to supply an electric current to a piezoelectric element PZT by an inductor storing energy and to operate the piezoelectric element PZT by discharging electric current from the piezoelectric element PZT.
This configuration makes it possible to reduce the power consumption of an NPN transistor 821 and a PNP transistor 822 of the electric current amplifier circuit.
JP-2009-292077-A discloses an image forming apparatus equipped with a drive signal generator circuit that improves energy efficiency by re-using the electric charge of the discharge from the piezoelectric element.
The drive signal generator circuit of JP-2009-292077-A mentioned above, as illustrated in FIG. 8, has a capacitor C2 charged by the electric charge from discharging of a piezoelectric element C1 and multiple switching elements including a switching element S2 that switches the connection of the terminal on the reference voltage side of the capacitor C2 between ground and a negative power source-E.
Also, since a driving current charge-discharge circuit 30c is provided which re-uses the electric charge charged at the capacitor C2 for the piezoelectric element C1, energy efficiency is improved.
However, although the inkjet recording device of JP-2001-063040-A mentioned above has the transformer 90 including the two coils of L1 and L2, it still requires a large-scale heat discharging and cooling mechanism because reducing the heat generation of the NPN transistor Q1 and the PNP transistor Q2 is insufficient.
Consequently, size reduction of the device is not to be expected.
Similarly, the liquid spraying device of JP-2011-046028-A mentioned above is successful in reducing the heat generation of an NPN transistor 821 and a PNP transistor 822, a circuit (drive signal generating unit 70) is newly added, so that here too size reduction of the device is not to be expected. Moreover, the image forming apparatus of JP-2009-292077-A mentioned above is successful in improving energy efficiency but two switching elements are newly added.
Since these switching elements generate heat, it is not possible to obviate the need for a heat discharging and cooling mechanism, which again limits the size reduction.
Unlike the inkjet recording device, any of the atomizer, the applicator, the powder manufacturing device, and the toner manufacturing device can discharge ink from all the nozzles simultaneously. For this reason, it is preferable to put all the channels (typically more than several hundred) provided to a liquid discharging device (head) together and drive them by a single drive signal generator circuit instead of switching all the channels on/off separately.
However, the driving current to operate the piezoelectric element is several hundreds of times as great as the case of switching all the channels on/off separately, which leads to a large amount of heat generation of the drive signal generator circuit.
Furthermore, different from the inkjet recording device, these devices continue discharging droplets during operation, which increases the amount of heat generated.